The movie subtitle appeared slower or faster within both Browser and media player programs

There are a bunch of web sites for watching movies free online with subtitles. I often use a browser add-on like Flash Video Downloader to download the movies for watching offline due to slow internet connection, which makes the video keep buffering and pausing like every 5 seconds. Note that the subtitles is not embedded in the video files so I have to download those subtitles from different sites so that I can add them in media player program like VLC. However, the subtitles i downloaded from english-subtitles.org and yifysubtitles.com didn't work correctly. The subtitles either appeared slower or faster than the videos. It's because almost all of the subtitles on the sites were made for different sizes of videos. For example, the videos on those free online sites were 720px HD but the subtitles were made for 480px HD or 1048px HD.

The only one that works for me so far is opensubtitles.org. This site has different subtitles uploaded by different author for different sizes of a video (480px HD, 720px HD, 1048px HD, and so on). Usually, the subtitles for 720px HD made by the author named Blueray is the default one. In other words, it will be downloaded when the user clicks on the Download button. And that one normally works. However, you can download other subtitles uploaded by other authors too and try them out.